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Consider a hollow aluminum sphere (assume 1 cm diameter, 1 mm wall thickness, filled with and surrounded by air) placed in a uniform magnetic field (assume 10-20 mT). Are there any realistic circumstances in which the magnetic field in the internal volume of the sphere is increased, rather then decreased?

This is not a homework question. One of the answers below says that aluminum is paramagnetic, and would shield the internal volume of the sphere from the magnetic field. It is also known that some common aluminum alloys (e.g. 6061) contain up to 1% ferrous metal. Could this magnetization of the sphere generate a field that exceeds the shielding? What is the likely size of that field?

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Aluminum is a paramagnetic material, so the magnetic field inside the walls of the shell should slightly increase at the expense of the magnetic field inside the shell and outside of the shell.

If the shell was made out of iron or steel, the field rerouting effect would be much stronger and the space inside the shell would be substantially shielded from the applied magnetic field, but the shielding mechanism would be the same as with an aluminum shell.

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  • $\begingroup$ Do you believe the magnetic field inside the sphere would always be weaker? Is there a possibility that the magnetization of (the paramagnetic) aluminum could slightly increase the magnetic field inside the sphere? $\endgroup$ – MichaelT Oct 12 '18 at 18:50
  • $\begingroup$ @MichaelT If that was the case, magnetic shielding would not work. $\endgroup$ – V.F. Oct 12 '18 at 18:51

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